hi.
The female will left up her front, and flip the "tail" open a little bit. With both claws extended, she will flop her "tail" and tens of the baby crabs will cames out. She will do this for many minutes, until all the babies are hatched. If you put them under a microscope, the babies look like a little shrimp with a big head.
After a few hours/days, all the juv. crab will be either eaten by other critter in the tank, or got chopped up by the pump.